The invention relates to a method for the production of industrial filament yarns by swirling a polyester multifilament at increased temperature, under a thread traction force of less than 140 cN, in an air-loaded swirl nozzle consisting of a nozzle body with a perforated plate and a baffle plate, and also to an apparatus for carrying out the method and to an industrial filament yarn.
Multifilament yarns are swirled during the spinning process, in order to obtain an intertwining of the individual filament fibrils and avoid spreading of the threads during further processing. Intertwining is carried out at particular points, and makes it possible to have improved cohesion of the individual filaments in the composite fibril structure and a greater capacity of the yarn for further processing.
Methods for the intertwining of the multifilament yarns are known, knotting taking place in a swirl duct or between two plates by means of an air jet. The number of knots can be controlled both via the pressure and via the velocity of the swirling air.
During the melt-extrusion of the polymers in the spinning process, oligomers always form and may be deposited from the surface of the multifilament yarn onto the cold baffle plate of the swirl nozzles due to the blowing action. These hard, often crust-like deposits may cause blockages in the air supply and in the takeup ducts and also fibril damage and may produce inadequate, unstable and irregularly arranged knots.
Industrial filament yarns made of polyester, in particular those which, in terms of the production method, are characterized by a low winding thread traction force of less than 100 cN, have a particularly strong tendency, in an overall linear density range of 500 to 2000 dtex, to form deposits in the swirl nozzle. By means of the known cold-air swirling, as described, for example, in EP-A-0,148,402, a commercially available open swirl nozzle with perforated plate and baffle plate can be kept in operation for up to a maximum of 24 hours. After that, the nozzle has to be cleaned mechanically and chemically in a complicated procedure.
In order to prolong the nozzle service life and achieve better knotting, knot distribution and swirling stability, hot swirling air has been used for producing such multifilament yarns. In this so-called hot-air swirling, cold compressed air is heated to about 290xc2x0 C. by an air heater installed in the compressed-air system. Improvements have been achieved, but they are unsatisfactory, particularly because of the irregular knot arrangement and the high energy consumption. Another disadvantage of hot-air swirling is that a complicated regulating system casts doubt on the viability of such a method.
The object of the invention is to provide a simplified method which makes it possible to have a better knot distribution and allows a prolonged nozzle service life.
Another object is to make available a swirl apparatus which reduces the energy consumption of the method during swirling.
Yet another object is to make available an industrial yarn which is better suited to weaving use. Weaving use refers, above all, to fabrics for tents, blankets, building membranes, awnings, projection screens and geotextiles which, as a rule, receive a coating.
The object is achieved, according to the invention, in that the heat is directly transmitted to the polyester multifilament and the air is directly transmitted, via the nozzle body, to a highly heat-conductive metal block which is connected directly to the baffle plate and in which a bore is provided for receiving a heating body. Improved spreading and knot distribution and also an enormous saving of energy of 85% are thereby achieved. The swirl nozzle, which is a cold point in the spinning process, is eliminated.
It is expedient to heat the baffle plate to a constant temperature of between 150 and 180xc2x0 C., in particular 150xc2x0 C. to 170xc2x0 C., preferably 160xc2x0 C. A temperature of below 150xc2x0 C. has the disadvantage of an increase in the deposits; the swirling properties do not improve any further at a temperature of more than 180xc2x0 C.
A swirl pressure of between 1.5 to 3.0 bar, in particular 1.8 or 2.8 bar, has proved expedient. A pressure of below 1.5 bar and above 3.0 bar has an adverse influence on optimum knotting. Either too low or too high a number of knots per meter is obtained.
The apparatus for carrying out the method consists of a swirl nozzle with a nozzle body, a perforated plate and a baffle plate. The baffle plate is expediently directly connected, flush, to a highly heat-conductive metal block, for example made of aluminum, in which a bore is provided for receiving a heating body. Electric resistance heating arrangements or any other space-saving heating arrangements are suitable as the heating body. What is essential is the direct contact between the baffle plate and the metal block.
A polyester filament yarn produced by the method according to the invention, having a winding thread traction force of less than 140 cN, in particular less than 100 cN, and with an overall linear density of 500 -2000 dtex, has, in addition to a strength of at least 70 cN/tex, along with a breaking elongation of less than 24%, an increased knot resistance of greater than 80% and a distance between 2 knots of greater than 4.0 cm. The polyester filament yarn is pre-eminently suitable for the production of coated fabrics for industrial purposes.